Communications systems (e.g., public switched telephone system, cable television, LANs—local area networks, etc.) have been rampantly deployed in the marketplace for a number of years to provide high-speed, broadband communications services. A significant factor in providing quality communications services is the reduction and/or elimination of interference (e.g., electromagnetic interference—EMI, spurious radiation/emissions, noise) in the communications medium that attenuates the received signal-to-noise ratio at the receiving end. To ensure this goal, a plurality of different communications media have been developed to help reduce the unwanted interference (e.g., coax, shielded twisted pair, optical fiber).
However, new communications services that allow power along with data to be delivered, via the communications medium, to a receiving communications device require even more stringent interference reduction measures to be taken. One exemplary power/data communications standard is the Power over LAN standard in accordance with the IEEE 802.3af Draft 3.0 February 2002 specification hereby incorporated by reference. This standard has been recently developed for LANs (e.g., Ethernet) allowing the service provider to deliver power and data over the communications medium (e.g., category 5—CAT 5 cable) to the receiving communications device via an input port (e.g., 8-pin RJ-45 port).
Although the standard does specify techniques to isolate the LAN power feed from the rest of the circuitry in the receiving communications device (DTE—data terminal equipment or PD—powered device), there is no mention of reducing and/or eliminating the spurious emissions potentially caused by the unused pins within the input port since only four of the eight pins may be used for power delivery and data communications (e.g., pins 1-3, 6). During power delivery from and data communications service with the provider, coupling (from spurious emissions) may occur from the LAN cable on to the unused pins in the input port and cause disruptions in the operation of the communications device (e.g., computing device, telephone, camera, wireless communications device, etc.). However, due to the detection phase of the standard, permanent termination of these unused pins is not a viable solution since the communications device must provide a pre-determined input impedance (e.g., signature) to the power supply equipment (PSE) of the LAN service provider to properly identify the communications device as standard-compliant before delivering power to the device. Therefore, permanent termination of the unused pins would alter the value of this pre-determined impedance and thus prevent injection of the necessary power to commence device operation.
Therefore, due to the problems arising from spurious emissions radiating from unused pins in a communications interface of a communications device that may not be solved by permanent termination, there is a need to provide dynamic termination of these unused pins while still allowing (regular) power delivery, via the interface, to the communications device to maintain (normal) operation of the communications device.